Cardiac abnormalities, including aortic root dilatation and mitral valve prolapse account for the vast majority of deaths in the Marfan syndrome. In 11 patients with Marfan syndrome comparing M-mode echocardiography with two-dimensional sector-scanning, both techniques were comparable in assessing aortic root dimension. However, two-dimensional echocardiography affords added capacity to visualize aortic root morphology and the diagnosis of mitral valve prolapse is enhanced using two-dimensional echocardiography.